Australian Graziers Value Sparse Trees in Their Pastures: A Viewshed Analysis of Photo-Elicitation

Abstract

The temperate grazing region of southeastern Australia is experiencing a rapid decline in tree cover that threatens key ecosystem functions. Graziers are stewards of most of the trees remaining outside reserves, and hold the power to reverse the decline. Influencing graziers’ decision making about vegetation management requires an understanding of their landscape values. We asked 25 graziers to photograph features they considered significant on their farms. Their choices were analyzed using viewsheds, the spatial delineations of all areas visible in a photograph. Photos taken by landholders depicted woody vegetation more often than would be expected by chance, particularly the isolated and scattered trees that are declining most rapidly. Grazier awareness and appreciation of isolated and scattered trees should be harnessed by policymakers keen to reverse their decline. More generally, our work demonstrates the utility of simultaneously employing photo-elicitation and quantitative viewshed analysis.

Keywords:

• Australia
• Lachlan catchment
• landholder values
• native vegetation
• New South Wales
• photo-elicitation
• photograph footprints
• photography
• ranchers
• viewshed analysis

Acknowledgments

This work was funded by the Australian Research Council and the Australian Government Department of Environment, Water, Heritage and the Arts, through a Commonwealth Environment Research Facilities “Significant Project.” The authors thank Dr. Andre Zerger and Garth Warren of CSIRO Sustainable Ecosystems, who created the woody vegetation layer. Thanks also to three anonymous referees for insightful comments and suggestions.

Notes

Water bodies were not included because of an anomaly of the dry Australian landscape: Most surface water is found in man-made dams featuring steep earthen walls, these rarely mapped, while the drainage lines that are mapped are typically intermittent at best.

For those unfamiliar with spatial data, this is what is called a “raster” analysis, which means that the unit of measurement is a square cell. Cells are usually referred to by their resolution in meters. Raster layers can be continuous, each neighboring cell containing varying values such as elevation. Rasters can also be discrete, where all the cells within a boundary like a farm are given a coded identifier. These discrete rasters can be used as “zones,” where each code represents an area of interest within which the values of another layer are summarized.

http://fennerschool.anu.edu.au/publications/software/anudem.php.

This methodological anomaly is supported by other statistics. We found property vegetation cover was inversely related to the proportion of farm area captured. Trees form obstacles, making viewsheds smaller. Hills also got in the way: The two roughest farms had low (4.3 and 4.7%) viewshed coverage.

At the time of writing, Kate Sherren was affiliated with the Australian National University, Canberra, Australia.